Walnut Fact Sheet

• Family: Juglandaceae
• Genus: Juglans
  • Commercially important species:
  • English or Persian walnut (nuts); Juglans regia
  • Eastern black walnut (timber); J. nigra
  • Northern California black walnut (rootstock); J. hindsii
  • Paradox (rootstock); J. regia X J. hindsii
• Related species: Pecan - Carya illinoinensis
• English or Persian Walnut Juglans regia
• Description: Deciduous tree; chambered pith; silver-grey bark; large pinnate leaves with (5)7-9 leaflets; irregularly dehiscent husk; monoecious; dichogamous; male flower = catkin, female flower = pistillate spike with 2(-5) flowers; wind pollinated; bearing habit terminal or lateral; generation time 2-7 years.
• Origin: Central Asia, Himalayas to E. Europe
• History of cultivation: Millennia
• Site requirements: Deep fertile soil, warm temperate climate, water availability. (Rain-free growing season reduces blight incidence.)

Cultivation in California

• History: Late 1700s Spanish missionaries bring hard- shelled walnuts to CA; 1860s-1870s introduction of "soft- shelled" walnuts and first commercial orchards; 1940- 1960 industry moves to northern CA.
• Yield: 2 - 3 ton/acre (CA average 1.25 ton/acre)
• Cultivars: Franquette, Hartley (most common), Payne, Vina, Chico, Howard, Sunland, Chandler (most common in new plantings), Tulare (new).
• Rootstocks: Paradox, highly recommended and vigorous; J. hindsii, old standard; J. regia, recommended only where blackline disease is epidemic.
• Propagation: Common - grafting or budding on seedling rootstock. Under investigation - rooting cuttings to produce clonal rootstock and own-rooted cultivars.
• Spacing: Standard = 30' X 30' (48 trees/acre), high density 24' X 24' (76 trees/acre), hedgerow 11' X 22' (180 trees/acre)
  Irrigation: Flood, solid set sprinkler, microsprinkler
• Training System: Modified central leader
• Nutrition: Deficiencies-nitrogen below 2.3%, potassium below 0.9%, zinc below 15ppm; Toxicities -boron over 300 ppm, sodium over 0.1%, chlorine over 0.3%.
• Harvesting: September-October when 95% nuts hullable. Trees are shaken, nuts swept into windrow, collected, hulled, dried to 8% moisture.
• Marketing: Quality standards and marketing policies determined by Walnut Marketing Board. One large cooperative (50%) and many independent handlers (50%) market walnuts. 35% exported. 1/3 marketed in shell, 2/3 marketed shelled.

Research

• Development of new cultivars through breeding and genetic engineering; Replacements for methyl bromide; Codling moth control; Blight control; Clonal propagation; Harvest molds
  
  • Integrated Pest Management for Walnuts. (1993) University of California Division of Agriculture and Natural Resources. Pub. 3270
  • Walnut Orchard Management. (in press) UC Division of Agriculture and Natural Resources. Pub. 21410
  • Maintaining the Competitive Edge in California's Walnut Industry: Trends, Issues and Challenges. (1994) Agricultural Issues Center, UC Davis

  Prepared by Dr. Gale McGranahan 1995